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    Alan Guth: What made the Big Bang bang

    Nearly 35 years ago, the MIT physicist figured out what made the Big Bang bang. Finally, there’s evidence.

    Essdras M Suarez/Globe Staff
    Essdras M Suarez/Globe Staff
    MIT physicist Alan Guth.

    There’s a moment near the start of Joseph Haydn’s classical masterpiece The Creation, after the bass soloist slowly sings, “In the beginning, God made Heaven and Earth,” and after the angelic choir softly joins in with “And God said: Let there be light.” There is silence, and then the choir returns to intone, almost mistily, “And there was light.”

    On that last word, “light,” the choir and orchestra explode in a fortissimo C-major chord to create an experience that is both gorgeous and transcendent.

    If you close your eyes, you can almost imagine the Big Bang erupting around you.


    Of that musical moment, the late physicist Victor Weisskopf once said, “There cannot be a more beautiful and impressive artistic rendition of the beginning of everything.” Weisskopf, a crucial figure in the development of both the atomic bomb and the nuclear disarmament movement that followed it, regularly played the oratorio for his students at MIT.

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    He was a lover of classical music. But on the cosmic question of how it all began, this giant of science knew there was another reason to seek insight from a deeply religious 18th-century composer. Weisskopf and his fellow 20th-century scientists fundamentally had no answer for how the universe began.

    The theory that came to be known as the Big Bang started its long gestation nearly a century ago. Eventually, it won the backing of science and, after it got its catchy name on a BBC broadcast in 1949, the general public. Today, most of us walk around assuming that the Big Bang explains how the universe began. But look at it closely, and you realize it doesn’t.

    The Big Bang theory offers an explanation for how the early universe expanded and cooled and how matter congealed, from a primordial soup into stars, planets, and galaxies. What it describes, then, is the aftermath of the Bang. But it is effectively silent on why or how that first massive expansion happened or where all the original matter came from.

    As Alan Guth, the physicist who holds the MIT professorship named after Weisskopf, puts it, “The Big Bang theory says nothing about what banged, why it banged, or what happened before it banged.” Guth has been using that line for years, and it almost always draws an appreciative laugh from his audience, whether that audience is made up of scientists or laypeople. It has a piercing quality to it, reminding us that we’d overlooked something that should have been obvious, like leaving the house with a freshly pressed shirt and perfectly knotted tie but no pants.


    Guth (rhymes with “truth”) has had opportunity to trot out some version of that line for more than three decades now, ever since he came up with his revolutionary prequel to the Big Bang theory. For most of that time, Guth, a short, slightly rumpled man who displays a refreshing mix of modesty and self-confidence, has been making his case in academic lectures. He began using flimsy overhead transparencies and later moved to PDFs, but the message has remained the same. He has continued to promote it with undiminished enthusiasm, even as observational evidence remained elusive and seemed unlikely to emerge in his lifetime, if ever.

    Then in March, he received an e-mail from Harvard astrophysicist John Kovac, who had spent a good chunk of the past eight years looking at data from highly sophisticated telescopes planted on the South Pole. “Dear Alan,” the e-mail began, “I am eager to talk to you about a topic that concerns both your research and mine. It is important and somewhat urgent, and I would be grateful if you would keep my request to speak with you confidential.”

    The next day, Kovac appeared in Guth’s MIT office, having used a back staircase to avoid detection. A week after that, Alan Guth, at age 67, became an academic celebrity, treated not just as a scientist who finally had backing for his theory, but also as a sort of seer who could help explain our place in the cosmos.


    Alan Guth
    “The Big Bang theory says nothing about what banged, why it banged, or what happened before it banged,” says Guth, pictured in younger days.

    PERHAPS YOU WENT TO SCHOOL WITH someone like Alan Guth, a child so preternaturally gifted that the teachers didn’t know what to do with him. He grew up in Highland Park, New Jersey, occasionally helping his father at the family dry cleaning business but clearly destined for greater things. In his junior year of high school, his physics teacher gave him a college textbook and sent him and a couple of other smart kids into a back room, telling them to teach themselves. Just before he took his high school sweetheart, Susan, to the junior prom, he was stunned to learn he wouldn’t be coming back for his senior year. His soon-to-be chemistry teacher, no doubt dreading a year of pesky questions he might not be able to answer, had conspired with the guidance office to get Guth accepted to MIT. So Guth said goodbye to Susan and Highland Park and headed for Cambridge.


    He continued to excel at MIT, earning his bachelor’s, master’s, and PhD in physics there. He carried that enormous promise with him when he left Cambridge at the dawn of the 1970s for a postdoctoral researcher position at Princeton. But by the end of that decade, his rapid ascent had reversed direction. He had cycled through a series of postdoc slots around the country, three years at Princeton, three years at Columbia, two years at Cornell, and a year at Stanford — elite shops, all of them, but despite his best efforts, he couldn’t land a job with any kind of future. He was starting to look like a dented can. When Guth asked one Cornell theorist to write him a recommendation for an assistant professor position, the man said the strongest letter he could honestly write would be “kindly but vague.”

    Alan Guth
    Guth was a postdoc at the Stanford Linear Accelerator Center in 1979 when he made his “SPECTACULAR REALIZATION” about the universe.

    Part of the problem had to do with his area of research. Rather than follow the postdoc playbook of concentrating on subjects likely to lead quickly to publishable papers, Guth let his curiosity guide him. He spent a lot of time wrestling with abstract mathematical problems relating to the theory of elementary particles. And when a fellow physics postdoc at Cornell, Henry Tye, approached him in 1978 with a puzzling question relating to the early universe, Guth began searching for an answer, even if it lay way outside his field. “I knew only a little about cosmology,” Tye recalls, “and Alan knew even less.” (While astronomy focuses on the observation and study of the planets, stars, and galaxies, cosmology explores the mysterious roots of the universe — and its future.)

    As it happened, two leading lights in cosmology gave talks at Cornell, deepening Guth’s interest in the field. For one of those talks, by Robert Dicke, a professor at Princeton, Tye arrived so late that the only seats available were way in the back. The room was hot, and he could barely hear the speaker, so he got nothing out of it. But Guth had arrived early, got a good seat, and took extensive notes. At home that night, he logged an entry in his diary about the talk, pronouncing it “fascinating.”

    What made it so was the Princeton professor’s identification of the “flatness problem” with the Big Bang theory. The flatness refers to the geometry of our continually expanding universe, where its mass density and expansion rate remain exquisitely balanced. If that balance tipped even slightly in either direction, the universe would either fly apart or collapse on itself. Yet because the universe has been expanding for 14 billion years, even slight variations in the beginning should have become exaggerated by now, to disastrous effect. Dicke pointed out that for our universe to look anything like it does today, at one second after the Big Bang, the number describing the balance would have to have been within 15 decimal places of one, lying in the minuscule interval between 0.999999999999999 and 1.000000000000001.

    Yet the Big Bang theory offered absolutely no explanation for how that exceedingly precise balance might have come about. It would seem crazy to assume that it was just a coincidence.


    Alan Guth
    Pictured, Guth and his son, Larry, and the notation of his late-night epiphany.

    ANOTHER TALK, BY THEN Harvard physicist and future Nobel laureate Steven Weinberg, convinced Guth that there was important science to be done pondering the universe’s first infinitesimal fraction of a second. Other researchers dismissed this as impossible to study and best left to science-fiction writers.

    And then there was that question that his postdoc pal Henry Tye had asked him. It concerned whether a new class of theories gaining traction in physics called grand unified theories would dictate the existence of something called magnetic monopoles. These are magnets with isolated North or South poles rather than normal equal-strength North-South poles. Working together, Guth and Tye concluded that the early universe should have been so overrun by magnetic monopoles that it would have collapsed.

    In the fall of 1979, Guth left Cornell for the Stanford Linear Accelerator Center, and he and Tye continued to talk by phone, hoping to get a publishable paper out of their monopole research. Their task was made harder because another young researcher had scooped them with a paper highlighting this monopole problem. So they were scrambling to salvage their work, hoping to write about possible solutions to the problem.

    Guth was living in a rented house in Menlo Park with Susan, his high school sweetheart who had become his wife, and their son, Larry, who was just shy of his second birthday. Weighing heavily on Guth’s mind were his dim prospects for landing a job the following year.

    Inspiration visited Guth around 1 a.m. on December 7, as Susan and Larry lay sleeping in the next room. Later that morning, he raced on his bike to work, setting a personal record of 9 minutes 32 seconds (Guth leaves very little in his life undocumented). After doing further number crunching relating to his early-morning epiphany, he wrote in large block letters in his notebook “SPECTACULAR REALIZATION,” drawing a double box around the words for emphasis.

    His theory was what he would come to call inflation, the exponential expansion of the universe within its first fraction of a second. (More on that later.) He phoned Tye at Cornell and excitedly told him that this inflationary model solved not just the monopole problem but also the flatness problem.

    At the time, Tye was preparing to leave for a long trip to his native China, so what he most wanted Guth to do was finish his revisions to their monopole paper. It was already far too long, and time was running short, so they agreed they wouldn’t include anything about inflation. Guth was disappointed that he couldn’t seem to get Tye excited about his new theory. What neither of them realized then, though, was that by sitting in the back for that Princeton professor’s lecture, Tye had completely missed the man’s explanation of the flatness problem. “When Alan told me he had solved the flatness problem,” Tye recalls, “I had no idea what he was talking about.”

    Before Tye left for China, Guth asked him whether he minded if he continued to work on this inflation idea and tried to publish a paper while Tye was gone. “Of course not,” Tye replied.

    At lunch at Stanford a few weeks later, Guth heard a few colleagues talking about another cosmology problem he’d never heard of. “The horizon problem” describes the implication of the Big Bang theory that the universe began in near-perfect uniformity, even if that would seem to be completely improbable. After a big bang, you would expect to get a clumpy universe, not one that is uniform in temperature and form, in every direction.

    Guth made more scratches in his notebook. Then, like a child amazed to learn that his skeleton key opens every door in the house, he was delighted to discover that his new inflationary model could solve this problem as elegantly as it had the others.

    On January 23, 1980, slightly more than a month after his “SPECTACULAR REALIZATION,” Guth took his model public, delivering a lecture at the Stanford Linear Accelerator Center. Among the attendees was Sidney Coleman, a respected Harvard physicist who was spending the year there. Afterward, he told Guth “every word was pure gold.”

    By the next day, Guth had a couple of job offers, as well as invitations to take his lecture to campuses across the country. Over the next few months, this long-neglected academic was suddenly hot again, with official and unofficial job offers pouring in from Harvard, Princeton, and a half dozen other universities. Still, his dream job was back at his intellectual home of MIT. But there were no physics teaching posts open there.

    In the spring, after the last stop on his lecture circuit, his hosts at the University of Maryland took him out to a Chinese restaurant. When he cracked open his fortune cookie, it read “An exciting opportunity lies just ahead if you are not too timid.” After mulling it over for a weekend, Guth picked up the phone that Monday morning and called someone he knew at MIT. Allergic to self-promotion, Guth mustered the confidence to let it be known that if MIT could find a position for him, he would be very interested in accepting it. The next day, MIT called back and offered him not an entry-level position as an assistant professor but rather a tenure-track associate professorship.

    In the matter of just a few months, his career trajectory had returned to warp speed. After accepting the offer from MIT to join the faculty in the fall of 1980, he spent the rest of his time at Stanford working on a paper describing his inflationary model.

    In June, however, he was alarmed to discover that one piece of his model didn’t hold up. While his skeleton key still opened the doors to solve the flatness and monopole problems, it got jammed inside the horizon problem’s keyhole.

    After his months-long run as the hot new property in the physics world, he felt a giant “Oh, crap” pit in his stomach, wondering if he might be headed back to obscurity. Still, he remained optimistic that a solution would emerge. “And I knew,” he says, “that at least I had already gotten the job at MIT.”


    Suzanne Kreiter/Globe Staff/File
    In March at the Harvard-Smithsonian Center for Astrophysics, a team of scientists announced the first direct evidence for the existence of cosmic inflation.

    ON THE LAST TUESDAY IN MARCH of this year, Alan Guth sits in the back seat of his Honda Accord. Susan is in the front passenger seat while their daughter, Jenny, is behind the wheel. Jenny (who did her graduate work in mathematical neuroscience) is 29 years old, so she wasn’t even born when Guth came up with the idea of inflation. Her brother, Larry, is now a 36-year-old mathematician and full professor at MIT.

    I’m riding in the back with Guth as we head to Harvard. There, he’ll be giving a talk with John Kovac of the Harvard-Smithsonian Center for Astrophysics who led the multi-institution team that came up with that long-elusive evidence. I ask Susan, a friendly woman who teaches English to adult foreigners, how comfortable she has become in explaining her husband’s work. “I don’t know the math, and I don’t know the fundamental science,” she says in a slow speaking style that her students must appreciate, “but if it’s well explained, I can follow the ideas.” Even after three decades of hearing her husband explain his theory, though, she admits that she still finds it difficult to grasp both the immensity of the universe that his theory suggests and the tininess of its starting point.

    She turns her head to face her husband. “Alan, you used to say it all started from this singularity that was much smaller than an atom and that it got as big as a grapefruit” during inflation. “But now you say it was a marble?”

    “That’s right,” he replies. “I’ve changed the grapefruit to a marble.” Then, in response to what sounds like whimsy with metaphors (but which is really the result of refined estimates from certain grand unified theories), he laughs, though Guth laughter is closer to a series of exuberant cackles.

    Here, in language that you, Susan, and I can understand, is how Guth’s model of the inflationary universe works: Using the theories of Einstein and others, Guth points out that at extremely high energies, there are forms of matter that upend everything we learned about gravity in high school. Rather than being the ultimate force of attraction that Newton and his falling apple taught us, gravity in this case is an incredibly potent force of repulsion. And that repulsive gravity was the fuel that powered the Big Bang.

    The universe is roughly 13.8 billion years old, and it began from a patch of material packed with this repulsive gravity. The patch was, as Susan notes, tiny — one 100-billionth the size of a single proton. But the repulsive gravity was like a magic wand, doubling the patch in size every tenth of a trillionth of a trillionth of a trillionth of a second. And it waved its doubling power over the patch about 100 times in a row, until it got to the size of that marble. All that happened within a hundredth of a billionth of a trillionth of a trillionth of a second. As a point of comparison, the smallest fraction of time that the average human can detect is about one-tenth of a second.

    Steffen Richter/Harvard University
    This lab, located three-quarters of a mile from the Geographic South Pole, houses the telescope that captured images corroborating Guth’s theory.

    The ingredients of what would become our entire observable universe were packed inside that marble. While the density of ordinary material being put through that kind of exponential expansion would thin out to almost nothing, a quirk of this repulsive-gravity material allowed it to maintain a constant density as it kept growing. But at a certain point — while the universe was still a tiny fraction of a second old — inflation ended. That happened because the repulsive-gravity material was unstable, and, like a radioactive substance, it began to decay. As it decayed, it released energy that produced ordinary particles, which in turn formed the dense, hot “primordial soup.” At that point, after Guth’s model has explained what banged, why it banged, and what happened before it banged, he takes a bow and lets the standard Big Bang theory take over from there.

    About a year after Guth joined the MIT faculty in 1980, the “Oh, crap” pit in his stomach finally went away. That’s when he received a preprint of a paper from Andrei Linde, a physicist in Moscow. Linde, who is now at Stanford, had figured out an ingenious way to use inflation to solve the “horizon problem” that had tripped up Guth. “It saved my model,” Guth says now.

    Guth and a few colleagues made another big advance the following year in a paper showing that inflation, which remained pure theory, could conceivably be proved. That’s because inflation would have left a unique imprint on the expanding matter of the Big Bang. And this imprint could be seen in the oldest light of the universe — that is, if modern science could build tools sophisticated enough to detect the imprint. But Guth doubted that would happen in his lifetime.

    Jenny pulls the Honda up to the edge of the Harvard campus and lets her father and me out before she and her mom continue the hunt for street parking, which in Harvard Square can sometimes feel as elusive as the universe’s ancient light. Guth blows a kiss to his wife and daughter and then begins his march to the Science Center.

    Before long, Guth and Kovac are standing together in front of a packed auditorium, with all 350 seats occupied, along with scores of students sitting on the floor, clogging the aisles, and another 150 or so in the next room watching on a closed-circuit feed. Faculty members, many of them graybeards on the back nine of their careers, crowd in the front, while a diverse collection of students fills the rest of the room.

    Physically, the two scientists are quite a contrast. The 43-year-old Kovac is tall and trim, with short brown hair, perfect posture, and the earnest presentation of a church youth director. At 67, Guth has a slight stoop that makes him look shorter, a glorious swoop of gray hair, and a navy blazer that is a bit too long in the sleeves.

    I never made it to Kovac’s office, but my guess is it’s orderly. Guth’s is a chaotic collection of piles. In fairness, though, it looks markedly better than it did back in 2005, when he won’s “messiest office” contest, which earned a free makeover of his MIT quarters by a design consultant. The designer clearly never made it to his home office in Brookline, though. There, an unruly pile of papers erupts from the center of the floor, calling to mind the mashed-potato mountain from Close Encounters of the Third Kind.

    Despite the physical differences between Guth and Kovac, their soft-spoken, polite personalities make them as complementary as their streams of research. Although back in 2006 scientists using a NASA satellite had produced a map of the early universe that strongly suggested Guth was on the right track with his theory, the new evidence from Kovac’s team is the kind of rock-solid confirmation that theoreticians dream of. While acknowledging that the findings will need to be corroborated, Guth calls the new data “fantastically secure results.”

    Gretchen Ertl
    “Dear Alan, I am eager to talk to you about a topic that concerns both your research and mine,” Harvard astrophysicist John Kovac (pictured), who led the team that found the evidence.

    In what another scientist termed “a telegram from the first moments of time,” Kovac’s team found the smoking gun for inflation: evidence of gravitational radiation, or more specifically, swirling patterns in the polarization of the cosmic microwave background. In the viewfinder of their telescope on the South Pole was light formed just 380,000 years after our universe banged onto the scene. And in that ancient light they detected gravitational radiation that is far older, having been emitted during the universe’s first fraction of a second of existence.

    In his Harvard talk, Guth employs the kind of fog-free language that made his 1997 book, The Inflationary Universe, understandable to readers without graduate degrees. After the talk, as a throng encircles Guth and both graybeards and young students begin peppering him with questions, I pull Kovac aside and ask what drew him to this research. “There are no bigger questions,” he says, than how it all began. Kovac’s own curiosity about inflation dates at least to his junior year of high school in Tampa, when he chose the geometry of the universe as the subject of an English term paper.

    Because of all the attention surrounding his research, he says, his 9-year-old son is now grappling with inflation. That’s the beauty of cosmology: Scientists working at the top of the field are on the hunt for answers to the questions rattling around in the brains of 9-year-olds.


    A FEW DAYS AFTER the Harvard talk, I walk with Guth into the basement of a two-story brick building at the edge of the MIT campus. It’s a lab for the Laser Interferometer Gravitational-Wave Observatory, which has sites in four states. Our guide is Nergis Mavalvala, a professor of astrophysics, who shows us a laser and a vacuum chamber housing a mirror so superbly stable that it moves about 100 million times less than the floor we’re standing on.

    The goal of the observatory is to detect the kind of gravitational waves that Einstein predicted nearly a century ago. They’ve been at work for about 20 years and have in total spent about $1 billion of federal research money. “We still haven’t seen one,” Mavalvala says.

    While that might lead some budget cutters in Washington to want to start slashing, she stresses that investment in science often takes time to pay out, but the rewards of patience can be tremendous.

    Guth knows that as well as anyone. He waited 35 years for evidence to support his theory. And he points out that it took nearly 50 years for proof of the “God particle,” the Higgs boson, a linchpin for physicists trying to fathom the mass and diversity of particles in the universe. That particle had been first theorized by British physicist Peter Higgs and others back in 1964, but it wasn’t until 2012 that scientists at the multibillion-dollar Large Hadron Collider found evidence of it. Last year, at age 84, Higgs shared the Nobel Prize in physics.

    It will probably take even longer to find evidence to support the breakthrough theories of tomorrow. “We’ve already understood,” Guth says, “the things that are close by” — the universe’s low-hanging fruit. “We have to wait.”

    A little while later, as we walk through a different building on campus, an emeritus professor spots Guth and flags him down. “You know that when you win a Nobel, you lose a year of your life,” the man says. “So get ready.”

    Guth flashes a polite but puzzled smile. I wonder whether this senior scientist is going to cite some kind of depressing actuarial table showing reduced lifespan for laureates.

    “You’ve been to the Nobel ceremony before, right?” he asks Guth.

    “Um, actually, I haven’t.”

    The man, who later asks me not to use his name, explains that he had traveled to Stockholm when a friend won. “First of all, it’s winter, and there’s no sun, so they get you drinking!”

    “Oh,” Guth replies. “I don’t drink very much.”

    “And then the Swedes have you speak at every damn college in the country,” he says. “They get their money’s worth!”

    By now, it’s clear that the man is not predicting a shortened life but rather a year of research lost to obligations of ceremony and speaking.

    This kind of Cambridge shoptalk doesn’t appear to be something Guth is eager to engage in. He’s a self-effacing guy. Besides, who wouldn’t worry about the possibility of jinxing himself by acting too presumptuous?

    Still, the prevailing view in the scientific community is that it’s hard to see how Guth won’t be one of the people getting an invite to Stockholm. Henry Tye, the former postdoc who put Guth on the path of inquiry that led to inflation, admits that he regrets he hadn’t grasped the significance of what his pal was trying to tell him back in 1979. But Tye, who went on to a distinguished career at Cornell that continues now in Hong Kong, says there can be no disputing how big a paradigm shift Guth’s inflationary model has made to science’s understanding of how it all began.

    Gretchen Ertl
    After a talk at MIT in April, Guth is mobbed by students and others with questions.

    Later that same day, over sodas in the Museum of Science cafe, I revisit with Guth the issue of the Nobel. Although it comes with a coveted $1 million-plus purse, Guth says that wouldn’t make a major difference in his life. Two years ago, he won a brand new award, the Fundamental Physics Prize, which came with a stunning $3 million check. Nonetheless, Guth continues to drive a Honda sedan. But he admits the psychic benefits of the Nobel would be enormously rewarding. “It would be a final confirmation,” he says, “that a large portion of the world feels that the theory is right.”

    And with proof that inflation is right, it starts to get even more interesting. In the lobby outside the museum planetarium, there’s a diorama display titled “Where in the Universe Are We?” It has a series of connected boxes, going from Earth to Solar System to Sun’s Neighborhood to Milky Way Galaxy to Local Group to Universe. Above the boxes is this message, “The universe is such an enormous place, it’s easy to get lost.”

    But in Guth’s mind, that message understates things to a staggering degree. We already know that our sun is just one of at least 100 billion stars in our galaxy and our galaxy is just one of 100 billion in the observable universe. But Guth says the most plausible models of inflation suggest something called eternal inflation. That means that once inflation starts producing universes, it never stops.

    And, by extension, Guth says, that would mean that we’re not just part of a vast universe, but that ours is merely one “pocket” universe in an ever-expanding multiverse. So if you’ve just come to terms with how infinitesimal a speck we earthlings are in the whole cosmic scheme of things, get ready to feel even smaller.

    At this point, Guth’s thinking on the multiverse remains just theory and is by no means universally accepted in the physics world. But it’s already drawn influential backers, and even those who haven’t fully signed on yet find themselves intrigued. “It’s a very attractive picture, very plausible, and it leads to very interesting consequences,” says Steven Weinberg, the Nobel laureate whose talk at Cornell helped inspire Guth. “But we don’t have any way now of confirming those theories.”

    Then again, that’s what people said about Guth’s revolutionary idea 35 years ago. So whether it takes 10 years or 50 years or 100 years for the evidence to emerge, the people who design the museum exhibits probably shouldn’t get too attached to their current signs presuming a single universe. As for the rest of us, rather than wallowing in our smallness, we might as well kick back and put on some Haydn to feel big once again.

    Neil Swidey is a Globe Magazine staff writer. E-mail him at and follow him on Twitter @neilswidey.